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Author Topic: VX with Weber 40DCNF - help!  (Read 3993 times)
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megaera
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« on: May 17, 2015, 12:08:41 PM »

Hello

I have only recently joined the forum and have loads of questions - however, this has to be the first, as I am getting more and more confused!

I want to improve things on the carb front - but keep it all looking as stock as possible. I am leaning towards a single Weber 40 DCNF, as I believe that will pop straight onto my stock manifold? Can anyone confirm this is so?

My main confusion is the whole single vs dual set up. I have read that lots of people use a dual set up with 2 x 40 DCNFs - can someone tell me how significant the gain would be over a single? Obviously, the cost is greater - an extra carb, modded manifold etc. But I am only looking for a general improvement for road use - no track stuff.

Also - if I went with the single - does anyone know the correct choke/jetting for it? What type air filter set up is recommended?

Thanks very much - I need all the advice I can get.

Additional info - I am getting a 4-1  3" SS sytem made up. Not stock, I know, but I feel the gains outweigh aesthetics  Wink
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rossocorsa
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« Reply #1 on: May 17, 2015, 01:55:37 PM »

single dcnf on a vx fits standard manifold and airbox you just need to make a steel plate to sit below the air cleaner intake on top of the carb as a dcnf has a narrower top than the 36dca due to the lack of auto choke. if you want real power you'd need a single dcoe on a custom manifold but then it all starts getting expensive and also doesn't look very original. you should also consider a standard inlet cam instead of the vx item. Are you sure that a 3 inch exhaust will fit, I thought about 2.5 was the max?
« Last Edit: May 17, 2015, 09:15:08 PM by rossocorsa » Logged
megaera
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« Reply #2 on: May 17, 2015, 06:03:42 PM »

Thanks for your great reply!

OK - can you explain why I should swop the camshaft? What do I gain over using the existing VX one?

What type of custom manifold would I need - does it need to be fabricated, or could a suitable one for a 40 DCNF be bought from someone like Guy Croft? Would anything else need to be changed - such as fuel pump, etc. or would it just be the manifold and presumably the air filter box?

On the exhaust - I must have misread it! I thought that was the recommended spec on Guy Croft's site. I am sure you are absolutely right - so the 4-1 2" would be correct?

I want a bit snappier performance - but not to the point where much other the the carb and manifold need changing. More of a mini tweak ......

Thanks so much for your help - appreciated!
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rossocorsa
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« Reply #3 on: May 17, 2015, 06:46:13 PM »

not sure on the exhaust 2.5 inch was what I remember but I could easily be wrong, if you are fitting a dcnf you can keep all the existing manifolds and plumbing so the car still looks almost original under the bonnet. The normal 2 litre inlet cam will give you more lift and duration the original vx inlet is quite mild probably in a not very successful  attempt to curb the horrendous fuel consumption. You could put a normal exhaust cam on as well but it would be like throwing buckets of petrol out the exhaust .....
the standard airfilter box will be fine, you could use a k&n filter in it if you want. This is the practical solution the more optimum solution is a bespoke inlet manifold plus dcoe this gives more power but you need to relocate a smaller radiator to make it fit and it is still tight I've decided against this on my car even though I did have all the parts to do it. Eric Weston may well be along soon to advise!   
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Neil-yaj396
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1979 1300 Coupe 1983 2000ie Coupe


« Reply #4 on: May 17, 2015, 08:32:56 PM »

I take it twin carbs can't be fitted to the Volumex?
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rossocorsa
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« Reply #5 on: May 17, 2015, 08:35:58 PM »

Never seen it done and with forced induction it's probably over kill anyway but there's not much space in the engine bay either, with the supercharger in between carb and cylinder head 
« Last Edit: May 17, 2015, 08:46:39 PM by rossocorsa » Logged
megaera
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« Reply #6 on: May 17, 2015, 08:46:06 PM »

Just as a matter of interest, if I were to put the 40 DCNF onto the standard manifold, with the 4-1 2" exhaust system - but no other modifications but a general tune up - could you hazard a vague guess as to the possible increase in bhp/performance?

Would the improvement be

1) Awesome
2) Impressive
3) Noticeable
4) Negligible

Thanks again - invaluable info!
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rossocorsa
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« Reply #7 on: May 17, 2015, 08:48:44 PM »

I suspect only slight, haven't finished mine so can't comment from experience yet!
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rossocorsa
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« Reply #8 on: May 17, 2015, 08:55:10 PM »

If you are serious you should buy Crofts latest book and take it from there, check with him the exhaust size I thought it was two and a half inch bore but he will confirm.
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rossocorsa
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« Reply #9 on: May 17, 2015, 09:17:06 PM »

single dcnf on a vx fits standard manifold and airbox you just need to make a steel plate to sit below the air cleaner intake on top of the carb as a dcnf has a narrower top than the 36dca due to the lack of auto choke. if you want real power you'd need a single dcoe on a custom manifold but then it all starts getting expensive and also doesn't look very original. you should also consider a standard inlet cam instead of the vx item. Are you sure that a 3 inch exhaust will fit, I thought about 2.5 was the max?

oops just noticed typo on my post!! corrected now apologies
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rossocorsa
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« Reply #10 on: May 17, 2015, 09:22:26 PM »

Just as a matter of interest, if I were to put the 40 DCNF onto the standard manifold, with the 4-1 2" exhaust system - but no other modifications but a general tune up - could you hazard a vague guess as to the possible increase in bhp/performance?

Would the improvement be

1) Awesome
2) Impressive
3) Noticeable
4) Negligible

Thanks again - invaluable info!

A standard vx is quite eager especially from low speeds I always found it difficult to avoid wheelspin when entering main road from a side road in a hurry due to the copious low down torque. Perhaps you need to treat yours to a careful tune up first? From what I have read you will only gain about 15bhp max using the standard inlet manifold   
« Last Edit: May 17, 2015, 09:32:56 PM by rossocorsa » Logged
WestonE
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« Reply #11 on: May 18, 2015, 09:27:23 AM »

A single DCNF a K&N in housing filter and a Strada Abarth 130TC inlet cam with a Beta 2000 IE exhaust cam with the timing at 118 degrees is what I would do. You would need Vernier cam wheels and you would cut and plug the Aux DS. On the exhaust 41mm ID primaries going to a 2.5 inch tailpipe would be good if you are building an exhaust. You might see 20BHP from this and 10ft lbs torque. I would heat clad the underside of the airbox and fit the Beta IE outer airbox removing the trouble some thermo flap on the VX and ensuring cold air feed.

The carb would need setting up on a rolling road and this would work best with a well prepared cylinder head. With the exhaust cam timed well you will not throw the fuel down the exhaust.

I have a running Montecarlo Volumetrico (very large Supercharger the VX big brother) so I feel I have good knowledge on this one.

Cheers

Eric       
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megaera
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« Reply #12 on: May 18, 2015, 09:42:42 AM »

Thank you so much for you reply!

I think most of what you suggested is "do-able" for me..... I would get the exhaust made up, though, as the Prospeed people are not far from me and they do amazing custom SS work.

I am not sure how problematic it would be to track down an Abarth inlet cam...? Gooogle and eBay!!

So, would you advise just fitting the DCNF straight on the stock manifold?

Thanks again. I'm definitely inspired to do this now......

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rossocorsa
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« Reply #13 on: May 18, 2015, 11:49:24 AM »

I think a beta 2000 inlet cam (I don't think it needs to be specifically off an i.e. although the exhaust does as you need the dizzy drive) would be a decent second best if you can't find an abarth item, no doubt Eric will confirm. Eric on cam timing I guess you are talking about full lift position?
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WestonE
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« Reply #14 on: May 18, 2015, 05:39:13 PM »

The Beta 2000 Inlet cam has 0.5mm less lift @ 9.5mm and would need to be timed FL @ 113 degrees giving 7/51 timing not the factory 106 degree setting with 13 /45 timing. This reduces LATDC (lift at TDC) so there is less pressure conflict. I had one of these fitted and we experimented on the rolling road at Storm Developments.

The Beta 2000 IE exhaust has the dizzy drive and 9.5mm lift. The Strada Abarth cams have 10mm lift and the inlet one will work on the exhaust side of the VX.

The issue with Supercharged cars is not having the cylinder pressure fighting the incoming charge or the mixture blown straight down the exhaust hence LATDC on the exhaust side at 1mm or less and probably 1.5mm on the inlet side.

Eric
PS with engine management and injection it is common to run 8-9PSI of boost with CRs at 10.5:1 and one of my work colleagues has just put a 9PSI turbo kit on his 10.8:1 MX5 seeing 300BHP and 234 ftlbs. The VX engine potential is limited by the control of the ignition and fuelling including the un-balanced inboard manifold for which I had a deflector developed. I had a new outboard manifold made for my VMET and I run 6 injectors including 2 outboard. 
   
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megaera
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« Reply #15 on: May 21, 2015, 10:24:52 PM »

So - thanks to all so far for the informative and helpful responses!

I am definitely going the 40 DCNF route. I appreciate this is the real "bottom of the ladder" modification, but with the custom headers and 2.5" pipe, I think it should be a good balance between better breathing/ performance - but still very stock in appearance.

So - the standard Weber 40 DCNF 12 is shipped ( I think? Please correct me if I'm in error) with the following spec

32mm Venturi
4.5 Aux
125 Main
220 Air corrector
F24 Emulsion
50 Idle
45 Pump
175. Needle
100 pump spill valve

Please can someone advise as to whether this is suitable for my VX - or do I need alternative choke/jetting?

Thanks for any and all help
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rossocorsa
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« Reply #16 on: May 21, 2015, 11:21:35 PM »

I think you will need to rejet the whole carb and also fit smaller chokes, Eric might be able to advise a starting point for settings I re-jetted mine and used 28mm chokes however despite not ever running the engine yet I don't recall the settings (I will have a note somewhere) which in any case may need tweaking once the engine is running.  
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megaera
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« Reply #17 on: May 22, 2015, 07:45:53 AM »

Thanks for that......

As you say, maybe Eric will advise.....? I am really not sure what to change and don't want to make any alterations until I have an idea of where to start!
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rossocorsa
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« Reply #18 on: May 22, 2015, 08:04:23 AM »

I think I would work on the rest of the car first and get everything 100% the concentrate on any tuning once there are no other headaches
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